Method and device for displaying graphic layers

ABSTRACT

A method for displaying graphic layers is provided. The method includes: receiving a plurality of graphic layers; assigning sequence numbers to the graphic layers according to an overlay order; and displaying the graphic layers in a sequence order according to the sequence numbers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to Chinese Patent Application No.201510868966.1 filed on Dec. 1, 2015 in the China Intellectual PropertyOffice, the contents of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

Field of the Invention

Aspects of the present invention relate generally to a method and adevice for displaying and merging graphic layers, and more particularly,to a method and a device for displaying and merging graphic layers on anAndroid platform.

Description of the Related Art

In the field of mobile devices, multimedia video playback functions havebecome an essential requirement.

In a multimedia video playback system applied in an Android platform, ahardware composer (Hwcomposer) sequentially processes graphic layerstransmitted from a SurfaceFlinger. A traditional implementation is forthe Hwcomposer to process the graphic layers sequentially in the Z-axisdirection, and then to tag each graphic layer according to a priority ofoverlay, bit-block transfer (blit) and fallback. However, a disadvantageof this implementation is that the Hwcomposer has to processes thegraphic layers according to the order in which the graphic layers aretransmitted from the SurfaceFlinger.

When the number of source graphic layers is greater than the number ofstreams supported by the display interface units (DIU), the sourcegraphic layers need to be merged. To ensure that the overlay order iscorrect, only adjacent graphic layers can be merged. A traditionalmethod may be for the graphic layers to be sequentially merged from thehighest graphic layer to the lower graphic layer in the Z-axisdirection, or the graphic layers are sequentially merged from the lowestgraphic layer to the higher graphic layer in the Z-axis direction, untilthe number of graphic layers matches the number of streams. Thedisadvantage of this method is that it is reliant on the Z-axis order ofthe graphic layers; therefore, the method may not be providing theoptimal performance.

In addition, the traditional Hwcomposer may use a large number ofstreams to achieve optimal performance. However, power consumption ofthe DIU is positively correlated to the number of streams. This causeshigh power consumption.

As the foregoing illustrates, a new method and a device for displayingand merging graphic layers in the Android platform may be desirable.

BRIEF SUMMARY OF THE INVENTION

A detailed description is given in the following embodiments withreference to the accompanying drawings.

A method and a device for displaying graphic layers are provided.

In a preferred embodiment, the invention is directed to a method fordisplaying graphic layers, comprising: receiving a plurality of graphiclayers; assigning sequence numbers to the graphic layers according to anoverlay order; and displaying the graphic layers in a sequence orderaccording to the sequence numbers.

In a preferred embodiment, the invention is directed to a device fordisplaying graphic layers. The device comprises a control circuit, aprocessor and a memory. The processor is installed in the controlcircuit. The memory is installed in the control circuit and isoperatively coupled to the processor. The processor is configured toexecute a program code stored in the memory to instruct a hardwarecomposer to: receive a plurality of graphic layers; assign sequencenumbers to the graphic layers according to an overlay order; and displaythe graphic layers in a sequence order according to the sequencenumbers.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more fully understood by reading thesubsequent detailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1 shows an alternative simplified functional block diagram of acommunications device according to one embodiment of the presentinvention.

FIG. 2 is a simplified block diagram of the program code shown in FIG. 1in accordance with one embodiment of the invention.

FIG. 3 is a schematic diagram of a principle framework outputting framesin an Android system according to one embodiment of the presentinvention.

FIG. 4 is a flow chart illustrating a method for displaying graphiclayers according to an embodiment of the invention.

FIG. 5 is a schematic diagram illustrating that the HWcomposer assignssequence numbers to the graphic layers according to an overlay order inaccordance with one embodiment of the present invention.

FIG. 6 is a flow chart illustrating a method for displaying graphiclayers according to an embodiment of the invention.

FIG. 7 is a flow chart illustrating a method for merging graphic layersaccording to an embodiment of the invention.

FIG. 8 is a flow chart illustrating a method for merging graphic layersaccording to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Several exemplary embodiments of the present disclosure are describedwith reference to FIGS. 1 through 8, which generally relate to a methodand a device for displaying graphics layers. It should be understoodthat the following disclosure provides various embodiments as examplesfor implementing different features of the present disclosure. Specificexamples of components and arrangements are described in the followingto simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. In addition, the presentdisclosure may repeat reference numerals and/or letters in the variousexamples. This repetition is for the purpose of simplicity and clarityand does not in itself dictate a relationship between the variousdescribed embodiments and/or configurations.

FIG. 1 shows an alternative simplified functional block diagram of acommunications device according to one embodiment of the presentinvention. In FIG. 1, the communication device 100 can be utilized forrealizing a user equipment (UE) (or an access terminal (AT). Thecommunications device 100 may include an input device 102, an outputdevice 104, a control circuit 106, a central processing unit (CPU) 108,a memory 110, a program code 112, a transceiver 114, and a graphicsprocessing unit (GPU) 116. The control circuit 106 executes the programcode 112 in the memory 110 through the CPU 108, thereby controlling theoperation of the communications device 100. The communications device100 can receive signals input by a user through the input device 102,such as a keyboard keypad, touch screen, or microphone (for voiceinput), and can output images and sounds through the output device 104,such as a screen or speakers. The transceiver 114 is used to receive andtransmit wireless signals, deliver received signals to the controlcircuit 106 wirelessly, and output signals generated by the controlcircuit 106 wirelessly.

FIG. 2 is a simplified block diagram of the program code 112 shown inFIG. 1 in accordance with one embodiment of the invention. In thisembodiment, the program code 112 includes an application layer 200, aLayer 3 202, and a Layer 2 204, and is coupled to a Layer 1 206. TheLayer 3 202 generally performs radio resource control. The Layer 2 204generally performs link control. The Layer 1 206 generally performsphysical connections.

The communications device provided in the embodiments of the presentinvention can implement methods illustrated in the embodiments of thepresent invention. In order to easily describe, only the related partsof the present embodiment are shown. The specific technical details areillustrated in the embodiments shown in FIGS. 3˜8 of the presentinvention.

FIG. 3 is a schematic diagram 300 of a principle framework outputtingframes in an Android system according to one embodiment of the presentinvention. As shown in FIG. 3, in the example of the Android system, theprocess that a user triggers to render frames in the communicationsdevice, such as a mobile phone, through respective application programs(hereinafter, referred to as “application”) and have the picturesdisplayed on the display screen comprises the following steps.

First, in the application layer, each application 301 to 304 performs arender operation according to its own application design. After therender operation is completed, each application transmits renderedgraphic layers 311˜314 to a SurfaceFlinger 320 which is responsible forrefreshing the screen in an application framework layer.

Next, in the application framework layer, the system can query a displayinterface unit (DIU) 340 which streams may be used via a Kernel layer(not shown in FIG. 3). For example, the HWcomposer 322 queries the DIU340 for streams 331 to 333 that can be used. The Surfaceflinger 320processes the graphic layers according to information configured by theapplication to determine which layer should be put as an underlayer,which layer should be put as a top layer, which layers should use blendeffects, and so on. Then, the Surfaceflinger 320 merges some graphiclayers rendered by some applications together, and transmits them to thestream 331. Next, the Surfaceflinger 320 merges some of the remaininggraphic layers together, and transmits them to the stream 332. Finally,the Surfaceflinger 320 merges the remaining graphic layer together, andtransmits them to the stream 333. The DIU 340 receives the streams 331to 333, and synthesizes (combines) all the streams 331 to 333 into aframe. It should be noted that, in some embodiments of the invention,the number of streams used by the DIU 340 may be extended to more thanthree or less than three, and the invention should not be limited towhat is shown in FIG. 3.

Finally, the DIU 340 transmits the frame to a display device 350 (whichincludes a display controller and a display screen). For example, butnot a limiting one, an LCD hardware (including an LCD controller and anLCD display screen) is used to display the final frame.

Specifically, the steps of the image processing performed by theHWcomposer 322 and the DIU 340 are that the central processing unit(CPU) of the communications device uses an algorithm to achievesynthesis strategies, and then drives a graphics processing unit (GPU)of the communications device to implement synthesis operations.

FIG. 4 is a flow chart 400 illustrating a method for displaying graphiclayers according to an embodiment of the invention. It should be notedthat the method is performed by the HWcomposer 322 of the FIG. 3. Instep S405, the HWcomposer receives a plurality of graphic layers drawnby at least one application. Next, in step S410, the HWcomposer assignssequence numbers to the graphic layers according to an overlay order. Instep S415, the HWcomposer displays the graphic layers in a sequenceorder according to the sequence numbers.

The step in which the HWcomposer assigns sequence numbers to the graphiclayers according to an overlay order in step S410 can be specified asfollows. The HWcomposer needs to judge whether a current graphic layeroverlays any other graphic layer. When the current graphic layer doesnot overlay at least one graphic layer, the HWcomposer assigns aninitial sequence number to the current graphic layer, wherein theinitial sequence number is a minimum sequence number. Or, when thecurrent graphic layer overlays at least one graphic layer, theHWcomposer assigns a first sequence number to the current graphic layer,wherein the first sequence number is a next sequence number after amaximum sequence number between sequence numbers of the at least onegraphic layer overlaid by the current graphic layer.

FIG. 5 is a schematic diagram illustrating that the HWcomposer assignssequence numbers to the graphic layers according to an overlay order inaccordance with one embodiment of the present invention. It is assumedthat the order of the source graphic layers in the Z-axis direction fromlow to high is A→B→C→D→E→F. As shown in FIG. 5, the graphic layer Coverlays the graphic layer B, the graphic layer D overlays the graphiclayers B and C, the graphic layer F overlays the graphic layer E. InFIG. 5, since the graphic layers A, B and E do not overlay other graphiclayers, the HWcomposer assigns an initial sequence number 0 to thegraphic layers A, B and E, wherein the initial sequence number is aminimum sequence number. The graphic layer C only overlays the graphiclayer B, so the HWcomposer assigns sequence number 1 to the graphiclayer C. The graphic layer D overlays the graphic layers B and C, so theHWcomposer assigns the next sequence number (i.e., sequence number 2)which is after a maximum sequence number (i.e., sequence number 1)between the sequence numbers of the graphic layers B and C overlaid bythe graphic layer D. The graphic layer F only overlays the graphic layerE, so the HWcomposer assigns sequence number 1 to the graphic layer F.Therefore, the graphic layers arranged in ascending order according tothe sequence numbers are A, B, E→C, F→D. It should be noted that thegraphic layers with the same sequence number are not in any particularorder. Therefore, for the sequence number 0, it has no effect on theHWcomposer processing the graphic layer A first or the graphic layer Efirst.

In one embodiment, the HWcomposer can further classify the graphiclayers into a plurality of groups according to the sequence numbers, andgenerates a group list corresponding to each group. In this embodiment,the group lists generated by the HWcomposer according to the sequencenumbers may be as shown in TABLEs 1.1˜1.3. It should be noted that, inthe group lists, the sequence numbers can be arranged in the Z-axisdirection in ascending order.

TABLE 1.1 Sequence number Graphic layer 0 A, B, E

TABLE 1.2 Sequence number Graphic layer 1 C, F

TABLE 1.3 Sequence number Graphic layer 2 D

FIG. 6 is a flow chart 600 illustrating a method for displaying graphiclayers according to an embodiment of the invention. It should be notedthat the method is performed by the HWcomposer 322 of the FIG. 3. Instep S605, the HWcomposer receives a plurality of graphic layers drawnby at least one application. Next, in step S610, the HWcomposer assignssequence numbers to the graphic layers according to an overlay order. Instep S610, the HWcomposer assigns a weight value to each graphic layeraccording to a manner. In one embodiment, the HWcomposer can use abit-block transfer (BLIT) performance to assign the weight values of thegraphic layers. The lower the BLIT performance of the graphic layer, andthe higher the weight, wherein the BLIT performance may be related toimage format, size, or whether the graphic layer is a video image, andso on. Generally. The larger the size of the image, the harder it is toperform the BLIT. In another embodiment, the HWcomposer can judgewhether two adjacent graphic layers vary. When the two adjacent graphiclayers are undirty graphic layers, the HWcomposer can assign a minimumweight to the two adjacent graphic layers.

Referring back to step S620, the HWcomposer establishes a layer orderaccording to the sequence numbers and the weight values. In step S625,the HWcomposer displays the graphic layers according to the layer order.

In this embodiment, step S610 is the same as the illustration of stepS410 of FIG. 4 described above, so the details of step S610 will beomitted. The step S620 that the HWcomposer establishes the layer orderaccording to the sequence numbers and the weight values can be describedbelow. The HWcomposer reorders graphic layers in an initial groupcorresponding to the initial sequence number according to the weightvalues in descending order. For the remaining groups, the HWcomposerjudges whether a weight value of the last graphic layer of each grouplist in the remaining groups is greater than a weight threshold. Whenthe weight value of the last graphic layer in the group list is greaterthan the weight threshold, the graphic layers in the group list arereordered according to the weight values in descending order. When theweight value of the last graphic layer in the group list is not greaterthan the weight threshold, the graphic layers in the group list arereordered according to the weight values in ascending order.

As an example of FIG. 5, it is assumed that the weight values of thegraphic layers A˜F are 1, 2, 6, 5, 4, and 3, respectively. TheHWcomposer may reorder the graphic layers of each group according to theweight values after generating the group list according to the sequencenumbers. In the initial group corresponding to the initial sequencenumber 0, the HWcomposer reorders the graphic layers A, B and E of theinitial group according to the weight values in descending order togenerate a new group list, as shown in TABLE 2.1.

TABLE 2.1 Sequence number Graphic layer 0 E, B, A

For the remaining groups, the HWcomposer needs to judge whether a weightvalue of the last graphic layer of each group list is greater than aweight threshold. In this example, it is assumed that the weightthreshold is 3. The weight value of the last graphic layer F of a grouplist corresponding to the sequence number 1 in TABLE 1.2 is 3, which isnot greater than the weight threshold. Therefore, the HWcomposerreorders the graphic layers C and F of the group list corresponding tothe sequence number 1 according to the weight values in ascending orderto generate a new group list, as shown in TABLE 2.2. Similarly, thegroup list corresponding to the sequence number 2 as shown in TABLE 2.3.

TABLE 2.2 Sequence number Graphic layer 1 F, C

TABLE 2.3 Sequence number Graphic layer 2 DAs shown in TABLEs 2.1 to 2.3 above, the layer order established by theHWcomposer according to the sequence numbers and the weight values is E,B, A→F, C→D.

In another embodiment, before displaying the graphic layers, theHWcomposer can further judge whether a layer number of the graphiclayers is greater than a number of streams supported by the DIU. Whenthe layer number is greater than the number of streams, the HWcomposerfinds at least one pair of adjacent graphic layers according to theweight values and the layer order and merges the pair of adjacentgraphic layers.

Take TABLEs 2.1˜2.3 as an example. The layer order is E, B, A→F, C→D. Itis assumed that the number of streams supported by the DIU is 4. Sincethe layer number is 6, the HWcomposer judges that the graphic layersneed to be merged at least twice. In this example, the HWcomposerselects the graphic layers which have the minimum weight value and areadjacent to perform the merging process. In the first merging process,the HWcomposer selects the adjacent graphic layers B and A which havethe weight values 2 and 1, respectively, and merges the graphic layer Bwith the graphic layer A. In the second merging process, the HWcomposermerges the merged graphic layer with the adjacent graphic layer F.Through this way, the HWcomposer can display the graphic layers E, C,and D which have larger weight values through an overlay manner, anddisplay the graphic layers B, A, and F through the BLIT manner toachieve best performance.

FIG. 7 is a flow chart 700 illustrating a method for merging graphiclayers according to an embodiment of the invention. It should be notedthat the method is performed by the HWcomposer 322 of the FIG. 3. Instep S705, the HWcomposer receives a plurality of graphic layers in acurrent frame. In step S710, the HWcomposer assigns sequence numbers tothe graphic layers according to an overlay order. In step S715, theHWcomposer judges whether a first graphic layer and a second graphiclayer vary in a period. When the HWcomposer judges that the firstgraphic layer and the second graphic layer do not vary in the period(“No” in step S715), in step S720, the HWcomposer merges the firstgraphic layer with the second graphic layer, wherein the first graphiclayer and the second graphic layer are the adjacent graphic layers.Finally, in step S725, the HWcomposer displays the graphic layers inorder of the sequence numbers. When the HWcomposer judges that the firstgraphic layer and the second graphic layer vary in the period (“Yes” instep S715), in step S725, the HWcomposer does not merge the firstgraphic layer with the second graphic layer, and directly displays thegraphic layers in order of the sequence numbers.

In this embodiment, step S710 is the same as the illustration of stepS410 of FIG. 4 described above, so the details of step S710 will beomitted. It should be noted that the step S715 that the HWcomposerjudges whether the first graphic layer and the second graphic layer varyin the period can be described below. The HWcomposer can use a geometricdistortion symbol transmitted from the Surfaceflinger. When theHWcomposer does not receive the geometric distortion symbol, theHWcomposer can judge whether a buffer corresponding to the first graphiclayer and a buffer corresponding to the second graphic layer vary. Whenjudging that the buffer corresponding to the first graphic layer and thebuffer corresponding to the second graphic layer do not vary, theHWcomposer judges that the first graphic layer and the second graphiclayer do not vary, and then merges the first graphic layer with thesecond graphic layer.

FIG. 8 is a flow chart 800 illustrating a method for merging graphiclayers according to an embodiment of the invention. It should be notedthat the method is performed by the HWcomposer 322 of the FIG. 3. Instep S805, the HWcomposer receives a plurality of graphic layers in acurrent frame. In step S810, the HWcomposer assigns sequence numbers tothe graphic layers according to an overlay order. In step S815, theHWcomposer assigns a weight value to each graphic layer according to amanner. In step S820, the HWcomposer establishes a layer order accordingto the sequence numbers and the weight values. In step S825, theHWcomposer judges whether a first graphic layer and a second graphiclayer vary in a period, wherein the first graphic layer and the secondgraphic layer are adjacent graphic layers. When the HWcomposer judgesthat the first graphic layer and the second graphic layer do not vary(“No” in step S825), in step S830, the HWcomposer merges the firstgraphic layer with the second graphic layer. Otherwise, in step S835,the HWcomposer does not merge the first graphic layer with the secondgraphic layer.

In this embodiment, step S810 is the same as the illustration of stepS410 of FIG. 4 described above, step S815 is the same as theillustration of step S615 of FIG. 6 described above, step S820 is thesame as the illustration of step S620 of FIG. 6 described above, andstep S825 is the same as the illustration of step S715 of FIG. 7described above, so the details of step S810, 815, S820 and 825 will beomitted.

In one embodiment, before performing the flow chart 700 and the flowchart 800, the HWcomposer can further judge whether an update timeexceeds a predetermined value. When the update time exceeds thepredetermined value, the HWcomposer triggers to update the currentframe.

By using the methods of FIG. 7 and FIG. 8, the HWcomposer can merge theundirty graphic layers. The undirty graphic layers can be displayedthrough a BLIT manner, and the graphic layers which vary can bedisplayed through an overlay manner. For example, it is assumed thatthere are 4 graphic layers. If the 4 graphic layers are displayed in theoverlay manner, 4 streams are needed. However, if there are 3 adjacentgraphic layers which are undirty graphic layers among the 4 graphiclayers, the HWcomposer merely uses 2 streams to display the graphiclayers. After the undirty graphic layers have been merged in theprevious frame, the HWcomposer can continue to use the merged graphiclayers merged in the previous frame to avoid performing the BLIToperation for improving performance and efficiency.

In addition, the central processing unit 108 can execute the programcode 112 to perform all of the above-described actions and steps orothers described herein.

Therefore, by using the method and device for displaying and merginggraphic layers of the present invention, the operational efficiency ofthe device can be increased according to the overlay order and thesequence of the graphic layers adjusted in accordance with the weightvalues. In addition, the present invention may further merge the undirtygraphic layers and set a predetermined value to update the currentframe, so that the number of streams used by the DIU can be reducedeffectively to achieve a power-saving effect.

Various aspects of the disclosure have been described above. It shouldbe apparent that the teachings herein may be embodied in a wide varietyof forms and that any specific structure, function, or both beingdisclosed herein is merely representative. Based on the teachings hereinone skilled in the art should appreciate that an aspect disclosed hereinmay be implemented independently of any other aspects and that two ormore of these aspects may be combined in various ways. For example, anapparatus may be implemented or a method may be practiced using anynumber of the aspects set forth herein. In addition, such an apparatusmay be implemented or such a method may be practiced using anotherstructure, functionality, or structure and functionality in addition toor other than one or more of the aspects set forth herein. As an exampleof some of the above concepts, in some aspects concurrent channels maybe established based on pulse repetition frequencies. In some aspectsconcurrent channels may be established based on pulse position oroffsets. In some aspects concurrent channels may be established based ontime hopping sequences. In some aspects concurrent channels may beestablished based on pulse repetition frequencies, pulse positions oroffsets, and time hopping sequences.

Those with skill in the art will understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those with skill in the art will further appreciate that the variousillustrative logical blocks, modules, processors, means, circuits, andalgorithm steps described in connection with the aspects disclosedherein may be implemented as electronic hardware (e.g., a digitalimplementation, an analog implementation, or a combination of the two,which may be designed using source coding or some other technique),various forms of program or design code incorporating instructions(which may be referred to herein, for convenience, as “software” or a“software module”), or combinations of both. To clearly illustrate thisinterchangeability of hardware and software, various illustrativecomponents, blocks, modules, circuits, and steps have been describedabove generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure.

In addition, the various illustrative logical blocks, modules, andcircuits described in connection with the aspects disclosed herein maybe implemented within or performed by an integrated circuit (“IC”), anaccess terminal, or an access point. The IC may comprise a generalpurpose processor, a digital signal processor (DSP), an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA) or other programmable logic device, discrete gate or transistorlogic, discrete hardware components, electrical components, opticalcomponents, mechanical components, or any combination thereof designedto perform the functions described herein, and may execute codes orinstructions that reside within the IC, outside of the IC, or both. Ageneral purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

It should be understood that any specific order or hierarchy of steps inany disclosed process is an example of a sample approach. Based upondesign preferences, it is understood that the specific order orhierarchy of steps in the processes may be rearranged while remainingwithin the scope of the present disclosure. The accompanying methodclaims present elements of the various steps in a sample order, and arenot meant to be limited to the specific order or hierarchy presented.

Use of ordinal terms such as “first”, “second”, “third”, etc., in theclaims to modify a claim element does not by itself connote anypriority, precedence, or order of one claim element over another or thetemporal order in which acts of a method are performed, but are usedmerely as labels to distinguish one claim element having a certain namefrom another element having the same name (but for use of the ordinalterm) to distinguish the claim elements.

While the invention has been described by way of example and in terms ofthe preferred embodiments, it is to be understood that the invention isnot limited to the disclosed embodiments. On the contrary, it isintended to cover various modifications and similar arrangements (aswould be apparent to those skilled in the art). Therefore, the scope ofthe appended claims should be accorded the broadest interpretation so asto encompass all such modifications and similar arrangements.

What is claimed is:
 1. A method for displaying graphic layers, comprising: receiving a plurality of graphic layers; assigning sequence numbers to the graphic layers according to an overlay order; and displaying the graphic layers in a sequence order according to the sequence numbers.
 2. The method for merging graphic layers as claimed in claim 1, wherein the step of assigning the sequence numbers to the graphic layers according to the overlay order further comprises: judging whether a current graphic layer overlays any other graphic layer; assigning an initial sequence number to the current graphic layer when the current graphic layer does not overlay at least one graphic layer, wherein the initial sequence number is a minimum sequence number; and assigning a first sequence number to the current graphic layer when the current graphic layer overlays the at least one graphic layer, wherein the first sequence number is a next sequence number after a maximum sequence number between sequence numbers of the at least one graphic layer overlaid by the current graphic layer.
 3. The method for merging graphic layers as claimed in claim 2, wherein the sequence numbers are assigned in ascending order.
 4. The method for merging graphic layers as claimed in claim 2, further comprising: classifying the graphic layers into a plurality of groups according to the sequence numbers; and generating a group list corresponding to each group.
 5. A device for merging graphic layers, comprising: a control circuit; a processor installed in the control circuit; and a memory installed in the control circuit and operatively coupled to the processor; wherein the processor is configured to execute a program code stored in the memory to instruct a hardware composer to: receive a plurality of graphic layers; assign sequence numbers to the graphic layers according to an overlay order; and display the graphic layers in a sequence order according to the sequence numbers.
 6. The device for merging graphic layers as claimed in claim 5, wherein the step that the hardware composer assigns the sequence numbers to the graphic layers according to the overlay order further comprises: judging whether a current graphic layer overlays any other graphic layer; assigning an initial sequence number to the current graphic layer when the current graphic layer does not overlay at least one graphic layer, wherein the initial sequence number is a minimum sequence number; and assigning a first sequence number to the current graphic layer when the current graphic layer overlays the at least one graphic layer, wherein the first sequence number is a next sequence number after a maximum sequence number between sequence numbers of the at least one graphic layer overlaid by the current graphic layer.
 7. The device for merging graphic layers as claimed in claim 6, wherein the sequence numbers are assigned in ascending order.
 8. The device for merging graphic layers as claimed in claim 6, wherein the processor further executes the program code to instruct the hardware composer to: classify the graphic layers into a plurality of groups according to the sequence numbers; and generate a group list corresponding to each group. 